Quinolizine derivatives are known to exhibit excellent antibacterial activities(see PCT publication No. WO 95/10519) However, some of the conventional quinolizine compounds have limited activities against Gram-positive bacteria, while other quinolizine derivatives exhibit the problem of poor water-solubility or side effects such as high cytotoxicity.
The present inventors have, therefore, endeavored to develop non-toxic compounds having a higher potency against a wide spectrum of bacteria; and have unexpectedly found that certain quinolizine carboxylic acid derivatives having an amine moiety at the 8-position of the 4-oxo-quinolizine nucleus exhibit a broad spectrum antibacterial activity and reduced cytotoxicity.